1. Field
This invention relates generally to methods, systems and apparatus for managing digital communications systems. More specifically, this invention relates to estimating the configuration of one or more channels or lines in a communication system such as a DSL system.
2. Discussion of Related Art
As Digital subscriber line (DSL) technologies provide potentially large bandwidth for digital communication over existing telephone subscriber lines (referred to as loops and/or the copper plant). “xDSL” and “DSL” are terms used to generally refer to digital subscriber line equipment and services, including packet-based architectures, such as ADSL, HDSL, SDSL, SHDSL, IDSL, VDSL and RADSL. DSL technologies can provide extremely high bandwidth over embedded twisted pair, copper cable plant and offer great potential for bandwidth-intensive applications. DSL services are much more dependent on line conditions (for example, the length, quality and environment of the copper loop) than traditional telephone services (typically using a bandwidth including frequencies up to about 4 kilohertz) compared to DSL services (using a bandwidth including frequencies up to 30 MHz).
While some local loops are in great condition for implementing DSL (for example, having short to moderate lengths with micro-filters or splitters installed and with no bridged taps and no bad splices), many local loops are not as suitable. For example, local-loop length varies widely, the wire gauge for a local loop may not be consistent over the length of the loop (having two or more different gauges spliced together), many loops do not have micro-filters or splitters properly installed, and many existing local loops have one or more bridged taps (a length of wire pair that is connected to a loop at one end and is unconnected or poorly terminated at the other end). Additionally, local loops may have bad splices or bad connectors, or they may have legacy devices (party-line systems, alarm systems, etc) connected in series with the loop. This type of line information is important to the evaluation of DSL systems and configurations and may mean that DSL loops differ and thus behave differently. Information may exist about individual lines, or can be determined using earlier techniques (for example, evaluation using voice-band measurement and loop-qualification methods). However, the accuracy of some of this information is questionable; it has been found that line quality varies widely, even among lines in the same group. Further, voice-band measurements do not always accurately reflect the DSL environment of loops. Therefore, techniques that evaluate a single line in each binder or other group, for example, and then extrapolate that information to all other lines in such a group, may not provide accurate information about those other lines or even the evaluated line itself.
Other techniques include characterizing DSL transmission lines using time-domain reflectometry, in which a predetermined test signal is sent from a point of origin to a DSL transmission line, the line reflects a portion of the signal back to the point of origin, and the reflected signal is analyzed to determine transmission line characteristics. In other situations, a reference loop might be analyzed and/or characterized to generate a transfer function and to model the effects of attenuation, noise, etc. on signals in the reference loop. Typically, one reference loop is selected in each binder or other group of lines and evaluated.
Systems, methods and techniques that permit modeling of DSL systems, including DSL binders and other groups, would represent a significant advancement in the art. In particular, management systems may provide only limited information nominally on the line and a system that could infer substantially more information from that limited information would represent a considerable advancement in the field of DSL service rates and associated ranges.